Hexafluoropropylene has been prepared by the pyrolysis of tetrafluoroethylene. This process has several disadvantages. Tetrafluoroethylene, which is itself difficult to prepare and purify, is an explosive compound, which must be stored and handled with the greatest care. The pyrolysis of tetrafluoroethylene inevitably makes some perfluoroisobutylene as a by-product, and this compound is extremely toxic and is costly to remove and destroy. Another preparative method for hexafluoropropylene is to make it simultaneously with tetrafluoroethylene by pyrolysis of CHClF.sub.2. The product also contains the toxic by-product perfluoroisobutylene, and the process provides a particular mixture of the two products, which may be different from the ratio of products desired by the user. Both of the above synthetic methods are carried out at high temperatures, so it is necessary to make the equipment from rare and expensive metals. Patents describing these processes include U.S. Pat. Nos. 3,873,630, 2,970,176, 3,459,818, 2,758,138, and U.S. Pat. No. 3,306,940.
U.S. Pat. No. 3,865,885 discloses a process which converts propylene to CF.sub.3 --CCl.dbd.CCl.sub.2 in two steps, the first being the formation of isopropyl fluoride. The yield to CF.sub.3 --CCl.dbd.CCl.sub.2 from isopropyl fluoride was 85%, using cobalt on carbon catalyst. Therefore, although the yield from propylene to CF.sub.3 --CCl.dbd.CCl.sub.2 in two steps was not disclosed, it could not be higher than 85%.
UK 1077932 describes a process which gives 81% yield from propylene to CF.sub.3 --CCl.dbd.CCl.sub.2 and recyclable intermediates, using a carbon catalyst.
U.S. Pat. No. 3,436,430 describes a process which provides chlorofluorinated propylene without a catalyst. The products were largely hydrogen-containing, even at 450.degree. C. and 2.9 seconds catalyst contact time.
U.S. Pat. No. 2,900,423 relates to the synthesis of hexafluoropropylene by hydrogenation of CF.sub.3 --CFCl--CF.sub.3 over a catalyst.
Fluorination (e.g. the reaction of a chlorinated hydrocarbon with 1-8 carbon atoms with HF to substitute F for Cl) is disclosed in U.S. Pat. No. 3,258,500.